How we keep data current
This page explains how Calculate.co.nz keeps every rate, threshold and rule behind its calculators accurate as New Zealand law and data change throughout the year. Twice a month, every source on our register, covering Inland Revenue, the Reserve Bank, Stats NZ, MBIE, MSD and Waka Kotahi, is checked for updates, and each finding, including "no change", is logged so nothing is left to chance. Where a figure has moved, it is corrected once in a shared data file rather than inside individual pages, so the update flows automatically to every calculator that relies on it instead of one tool being fixed while another is missed. Before anything goes live, worked examples are re-checked against the new figures and automated tests run across the library to catch broken logic or stale numbers. You can see the result on any calculator page as a last-reviewed date, and on this page as a review cadence and history showing when the site was last checked rather than asking you to take it on trust. Certain dates, such as the 1 April tax-year change, the May Budget and Official Cash Rate decisions, trigger an extra review outside the normal cycle. If you ever spot a figure on the site that looks wrong or out of date, use the contact page to flag it and it will be checked and corrected.
The twice-monthly review cycle
Twice a month, every authoritative source on our register is checked for change. The review runs on a fixed fortnightly cadence so nothing depends on chance discovery, and the date of each review is recorded.
- 1. Scan the source register. Each source on the register (see below) is checked for new rates, thresholds, legislation, determinations or published figures since the last review. Findings, including "no change", are logged so the absence of an update is itself recorded.
- 2. Triage what changed. Any change is assessed for impact: which calculators, guides and datasets depend on that figure, how material the change is, and when it takes effect (some changes are dated for a future start, such as a 1 April rate).
- 3. Update the single source of truth. Shared figures live in central data files, so a rate is defined once. The change is made there and flows automatically to every tool that references it, which removes the risk of updating one calculator and missing another.
- 4. Validate. Worked examples are re-checked so each tool's output still matches its source, and automated checks run across the library to catch broken logic, missing structured data or values that drifted.
- 5. Record and date. The update is version controlled with a dated entry, the affected pages carry a last-reviewed date, and the change is reflected in the public library history.
Principles behind the process
- Single source of truth. Each rate or threshold is stored once and reused everywhere, so the whole site moves together when it changes.
- Data separated from presentation. The numbers live in data files, not buried inside individual pages, which makes them auditable and safe to update at scale.
- Provenance. Every figure is traceable to the official source it came from, so it can be re-verified rather than taken on trust.
- Scheduled change detection. A fixed fortnightly cadence plus event triggers, rather than waiting for someone to notice.
- Validation before publish. Worked-example checks and automated tests confirm a change is correct before it goes live.
- Visible freshness. Last-reviewed dates and a public change history show the work, rather than asking you to assume it.
Event triggers between scheduled reviews
Some dates always warrant a fuller review, and these are handled as they occur rather than waiting for the next cycle:
- The 1 April tax-year rollover, when many IRD rates, thresholds and ACC levies change.
- The annual Budget in May, and any in-year tax or benefit announcements.
- Official Cash Rate decisions and other RBNZ updates that affect interest and mortgage tools.
- Minimum wage changes, benefit and superannuation adjustments, and new or amended legislation.
The sources we track
| Source | What we track from it |
|---|---|
| Inland Revenue (IRD) | Income tax brackets, PAYE, GST, ACC earner rates, KiwiSaver settings, student loan thresholds, FBT, RWT, Working for Families, FIF rules |
| Reserve Bank of New Zealand (RBNZ) | Official Cash Rate, LVR and DTI settings, published interest rate data |
| Stats NZ | Inflation (CPI), wage and earnings data, household statistics |
| MBIE | Minimum wage, tenancy and employment settings |
| Ministry of Social Development (MSD) | Benefit rates, NZ Superannuation, accommodation support |
| Waka Kotahi NZ Transport Agency | Road user charges and vehicle-related figures |
| Legislation | The underlying Acts and regulations that define the rules each tool implements |
If something is still wrong
No process is perfect. If you spot a figure that looks out of date or incorrect, please tell us and it will be checked and corrected promptly. How the tools are built is set out in our editorial standards.
Review cadence: twice monthly. This page last reviewed 2026-09-09. Maintained by James Graham.